function changeTabs(idNum) {
  var classMatch = new RegExp("(^|\s)tab_(\d+(\s|$))");
  var showtabs = new RegExp("(^|\s)tab_" + idNum + "(\s|$)");
  var tag = "*";
  var elementID = document.getElementById("storybox");
	var elements = (tag == "*" && elementID.all)? elementID.all : elementID.getElementsByTagName(tag);
	var tab_Classes = [];
	var current;
	var length = elements.length;
	for(var i=0; i<length; i++){
		current = elements[i];
		if(classMatch.test(current)){
			tab_Classes.push(current);
		}
	}

  length = tab_Classes.length;
	for(var i=0; i<length; i++){
 		current = tab_Classes[i];
    if (showtabs.test(current.className)) {
      current.style.display = 'block';
    }
    else {
      current.style.display = 'none';
    }
  }
}